Audible indicator circuit



NOV. 30, 1965 W` FERRIGNQ, JR 3,221,317

AUDIBLE INDICATOR CIRCUIT Filed vJune 27, 1962 INVENTORZ WILLIAM L. FERR\GNO,JR.

BY WW@ wf Hls ATTORNEY.

United States Patent O 3,221,317 AUDIBLE INDICATGR CIRCUIT William L. Ferrigno, Jr., New Hartford, N.Y., assignor to General Electric Company, a corporation of New York Filed June 27, 1962, Ser. No. 205,590 4 Claims. (Cl. 340-220) This invention relates to indicator or alarm circuits, and particularly to such circuits which produce an audible sound in response to a predetermined input function.

The indicator circuit of the invention is useful as a sensitive indicator of light or light level; change in brightness; sound; rain or other moisture; voltage; current; and also is useful for indicating other phenomena that are, or can be converted into, electrical signals.

Previously known audible indicators have generally employed a relay, either of the electromechanical type or of the gas discharge tube type, connected to actuate a bell or buzzer in response to an input function or signal.

An object of the invention is to provide a new and improved audible indicator circuit.

Another object is to provide an audible indicator circuit that requires neither a relay, bell nor buzzer.

A further object is to provide an audible indicator circuit which provides a pleasing and controllable audible sound in response to input functions or signals.

A still further object is to provide a battery operated audible indicator circuit which is conservative of battery power.

Still other objects will be apparent from the following description and claims, and from the accompanying drawing.

The single ligure of the drawing is an electrical schematic diagram of a preferred embodiment of the invention.

The invention comprises, brietly and in its preferred embodiment, an electrical oscillatorcircuit arranged t oscillate in the audio frequency range when stimulated into oscillation by an electrical signal, and having a loudspeaker connected to the oscillator, either directly or via an amplifier, so as to produce audible sounds when the oscillator is oscillating. As a further feature of the invention, an amplifier stage for the loudspeaker is normally biased to cut-off in the absence of oscillation by the oscil lator, thereby conserving battery power.

The schematic diagram of the drawing is, for convenience, provided with dotted lines to separate portions of the circuit comprising a battery power supply 11, a signal input circuity 12, an oscillator circuit 13, and an output ampliiier and loudspeaker circuit 14. The battery powersupply 11 comprises a battery 16, which may comprise a pair of series connected flashlight batteries, thereby providing 3 volts, for example. The positive terminal of the battery is connected to an electrical ground wire 17 via a normally closed push button switch 18 which comprises a contact bar 21 normally urged against a pair of contact terminals 22, 23 by means of a helical compression spring 24 positioned around a plunger rod 26 between a push button 27 and a chassis housing or support plate 28. The negative terminal of the battery 16 is connected'to a negative potential supply wire 31.

The actuating or input signal circuit 12 comprises a transistor 32 having an emitter electrode 33 connected to electrical ground 17 via a series-connected single-pole, single-throw switch 34 and a variable resistor 36, A low impedance microphone means 37 which may be a loudspeaker used as a microphone is connected across the terminals of the switch 34. As shown, the microphone 37 comprises a loudspeaker consisting of a cone 38 and voice coil 39, the latter being electrically connected across the terminals of the switch 34.

3,221,317 Patented Nov. 30, 1965 ice A singlepole, single-throw switch 41 and a variable resistor 42 are connected in series between base electrode 43 of the transistor 32 and a negative voltage supply wire 31. A photocell 46 and a single-pole, single-throw switch 47 are connected in series across the variable resistor 42. A moisture detector 48 is connected across the switch 41, and may comprise any of the various known types of moisture detectors, such as a pair of metal screens or perforated plates arranged close together and parallel to one another, or a moistureabsorbing material such as cloth or paper provided with electrodes on the opposite surfaces thereof.

The oscillator circuit 13, as shown, comprises a multivibrator circuit having a pair of transistors 51 and 52. Emitter electrodes 53 and 54 of these transistors are connected to electrical ground 17. Collector electrodes 56, 57 of these transistors are connected to the negative voltage supply wire 31 via resistors 58 and 59, respectively. The base 61 of transistor 51 is coupled to the collector 57 of transistor 52 via a capacitor 62, and the base 63 of transistor 52 is coupled to the collector 56 of transistor 51 via a capacitor 64, in the well-known crosscoupling manner. The base electrode 63 is connected to the negative voltage supply wire 31 via a resistor 66, to provide a suitable bias voltage. The base 61 of transistor 51 is directly connected to the collector electrode 67 of the input transistor 32.

The output amplifier stage and loudspeaker circuit 14 comprise an amplifier transistor 71 having a base electrode 72 connected directly, for passage of direct current, to the collector electrode 57 of transistor 52. The emitter 73 of amplifier transistor 71 is connected to electrical ground 17 via a resistor 74. The collector electrode 76 of ampliiier transistor 71 is connected to the negative voltage supply wire 31 via a loudspeaker 77.

The operation of the circuit will now be described generally, and then will be described more specifically. With the oscillator circuit 13 in nonoscillating condition, no sound will be produced by the loudspeaker 77. The input circuit 12 is adjusted so that, upon the occurrence of a predetermined function or event, as will be more fully described later, current low in the input transistor 32 will be such as to cause the voltage at the collector 67 thereof to bias the multivibrator transistor 51 so that the multivibrator 13 will oscllate in a well-known manner. The oscillation frequency of the multivibrator 13,

`as determined primarily by the values of the resistors 58 and 59, and the cross-coupling capacitors 62 and 64, is chosen to be in the audible range, and preferably in a frequency range lying between the frequencies of cycles per second and 5000 cycles per second, a frequency of about 500 cycles being preferred. An oscillatory electrical signal thus produced is obtained at the collector 57 of transistor 52, and is applied to the base 72 of the amplitier transistor 71, whereupon this signal is amplified and applied to the loudspeaker 77, which produces an audible sound having a fundamental frequency the same as that of the oscillation frequency of the oscillator 13.

The multivibrator circuit, as shown, produces a squarev wave type of signal, which is rich in harmonics, and which produces a rich and pleasing sound at the loudspeaker 77. The multivibrator circuit components are given values such that the collector electrode 57 will have a potential, when the multivibrator is not oscillating, to bias the base electrode 72 of the amplifier transistor 71 for rendering this transistor in cutoti condition, and will have a different potential when the multivibrator is oscillating, of a value to bias the base'72 to render the transistor 71 conductive for amplifying the oscillatory signal.

The circuit arrangement, as shown, is such that, due to the direct coupling between the collector 57 of transstor 52 and the base electrode 72 of amplifier transistor 71, the amplifier transistor 71 will be biased at or beyond cutoff when the oscillator circuit 13 is not oscillating, whereby the amplifier transistor 71 draws no appreciable current from the battery 16 when the circuit is inoperative, thereby conserving battery power.- When the oscillator circuit 13 is oscillating, the oscillatory signal that is applied to the base electrode 72 of the amplifier transistor 71, biases the transistor 71 alternately on and off, whereby it draws current from the battery 16 only as needed to produce the sound at the loudspeaker 77.

The input actuating circuit 12 will now be described in greater detail. The variable resistors 36 and 42 are variable over a sufficiently wide range of resistance so that, by adjusting them, the input circuit transistor 32 can be biased to the off or non-conducting condition, or, alternatively, so that the transistor 32 has a quiescent collector current such that the multivibrator 13 will not oscillate.

The three alternative sources of input function, as shown in the drawing, viz., the photocell light detector 46, the moisture detector 48, and the sound detector 37, will now each be described in turn. The circuit functions as a light or brightness detector, when the switch 47 is closed and the variable resistance 42 is adjusted to a relativelylarge value, whereupon the base bias of the transistor 32 is varied rather greatly as a function of thev resistance of the photocell 46, which in turn is a function of light or brightness falling on the photocell 46. The variable resistor 36 is adjusted to a value such that light below a certain brightness level will not cause suicient current to flow in the input transistor 32 to trigger the multivibrator 13 into oscillating condition. Then, upon the occurrence of a light value exceeding the aforesaid value, the collector current of the input transistor 32. will increase and apply a forward bias to the multivibrator transistors 51 and 52, which will set the multivibrator circuit 13 into its oscillatory condition.

The type of multivibrator circuit shown in the drawing is such that the multivibrator will continue oscillating after the stimulus or triggering signal ceases. To turn the oscillator off, the push button 27 may be manually pressed, thereby momentarily opening the switch 18 and removing battery voltage from the circuit. Alternatively, the variable resistor 36 could be temporarily turned to its high resistance value in order to stop the oscillation of the multivibrator 13. Typical light sources that could affect the phototube 46 to set off the multivibrator 13 and thereby produce audible sound at the loudspeaker 77 are the occurrence of daylight, or the turning on of room lights, a burglars ashlight, etc. When the photocell 46 is not used as an input signal device, the switch 47 should be turned to its open-circuit position.

When the circuit is used as a rain or moisture detector the switch 41 is placed in its 0pm placing the moisture detector 48 in series with the base electrode 43 of the input transistor 32. The variable resistor 36 is adjusted so that the multivibrator 13 is normally nonoscillatory but will be rendered oscillatory in response to moisture appearing or occurring between electrodes of the moisture detector 48 thereby applying an actuating voltage to the base electrode 43 of input transistor 32 from the negative voltage supply wire 31. Sensitivity of the circuit to moisture can be controlled by adjustment of the variable resistor 42. Typical placement of the moisture detector 48 may be outside, whereupon the circuit produces audible sound in response to the occurrence of rain, or adjacent an open window to provide audible indication of rain blowing through the window, or the moisture detector 48 may be placed on an infants bed to indicate the occurrence of moisture and produce an audible sound to awake the infant upon the occurrence of moisture, thereby aiding in infant training. The moisture detector 48 may be positioned in a liquid storage tank to indicate when the tank is filled to a proper level, and may also be used in numerous other applications. When the circuit is not in use as a moisture detector, the switch 41 is thrown to its closed condition, as shown in the drawing.

When use as a s ect he switch 34 is thrown to the open position, thereby placing the microphone means 37 in series with the emitter 33 of input transistor 32. The variable resistors 42 and 36 are adjusted so that the multivibrator 13 will normally be nonoscillatory. Upon the occurrence of noise, the microphone 37 produces a signal at the emitter electrode 33, which is amplified and applied to the multivibrator 13, thereby causing the multivibrator to oscillate and produce an audible sound at the loudspeaker 77. Typical applications of the circuit of the sound detector would be to indicate a baby crying, the arrival of an' automobile in the driveway of a home, or to respond to the bark of a dog or meow of a cat, etc. When the circuit is not in use as a sound detector, the switch` 34 is thrown to its closed position, as shown in the drawing.

The frequency of the audible sound produced at the loudspeaker 77 may readily be adjusted by varying the values of the resistors 58 and 59. If desired, ganged variable resistors may be provided, whereby increasing these resistance values will cause the oscillator 13 to oscillate at a lower frequency, and vice versa.

In lieu of being provided with three different input means as described above, the circuit of the invention may be provided in kit form so that it may be constructed with either or any one of the signal input sources 46, 48 and 37. Alternatively, the circuit may be provided with suitable electrical jacks, into which the photocell 46, moisture detector 48, or sound detector 37 may be plugged.

While a preferred embodiment of the invention has been shown and described, various other embodiments and modifications thereof will become apparent to those skilled in the art, and will fall within the scope of the invention as defined in the following claims.

What I claim is:

1. An audible indicator circuit comprising a voltage Source, an input transistor having base, emitter and collector elec-trodes, a first variable impedance circuit connected between said base electrode and a first terminal of said voltage source, a second variable impedance circuit connected between said emitter electrode and a second terminal of said voltage source, a multivibrator having a pair of transistors each provided with base, emitter and collector electrodes, means connecting said lastnamed emitter electrodes to said second terminal, irnpedance means respectively connecting said last-named collector electrodes to said first terminal, a pair of capacitors respectively connected to cross-couple said lastnamed base and collector electrodes of the pair of multivibrator transistors, the values of said impedance means and capacitors being such as to cause said multivibrator to oscillate at an audio frequency, means connecting the collector electrode of said input transistor to the base electrode of a first one of said multivibrator transistors, an amplifier transistor having base, emitter and collector electrodes, means directly connecting the last-named base electrode to the collector electrode of the second one of said multivibrator transistors, said collector electrode of the second multivibrator transistor having a first potential when the multivibrator is not oscillating of a value to bias said last-named base electrode for rendering said amplifier transistor substantially in a cutoff condition and having alternate first and second values of potential when the multivibrator is oscillating to alternate the bias of said last-named base electrode for alternately rendering said amplifier transistor in a current-conducting signal-amplify-- 3,221,317 5 6 circuits thereby causing said multivibrator to oscillate and References Cited bythe Examiner produce an audible sound at said loudspeaker. I ED PA N 2. A circuit as claimed in claim 1, in which said rst' UN T STATES TE TS Variable impedance Circuit comprises a photocell for vary- 218201959 1/1958 Ben 340-213 ing the impedance thereof in response to light. 5 219421110 6/1960 LehOVeC- 3. A circuit as claimed in claim 1, iii-it/"Hi'ch said first 219691486 1/1961 Amfahl'- variable impedance circuit comprises a moisture detector 219741424 3/1961 Roberts 340-384 X for varying the impedance thereof in respr'tf moisture. 310411502 6/1962 FQSeT- 4. A circuit as claimed in claim 1, in which said second 310651309 11/1962 Glol'dvariable impedance circuit comprises a microphone means for varying the impedance thereof in response to sound. NEIL C READ Pnmary Exammer 

1. AN AUDIBLE INDICATOR CIRCUIT COMPRISING A VOLTAGE SOURCE, AN INPUT TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELECTRODES, A FIRST VARIABLE IMPEDANCE CIRCUIT CONNECTED BETWEEN SAID BASE ELECTRODE AND A FIRST TERMINAL OF SAID VOLTAGE SOURCE, A SECOND VARIABLE IMPEDANCE CIRCUIT CONNECTED BETWEEN SAID EMITTER ELECTRODE AND A SECOND TERMINAL OF SAID VOLTAGE SOURCE, A MULTIVIBRATOR HAVING A PAIR OF TRANSISTORS EACH PROVIDED WITH BASE, EMITTER AND COLECTOR ELECTRODES, MEANS CONNECTING SAID LASTNAMED EMITTER ELECTRODES, MEANS CONNECTING SAID LASTPEDANCE MEANS RESPECTIVELY CONNECTING SAID LAST-NAMED COLLECTOR ELECTRODES TO SAID FIRST TERMINAL, A PAIR OF CAPACITORS RESPECTIVELY CONNECTED TO CROSS-COUPLE SAID LASTNAMED BASE AND COLLECTOR ELECTRODES OF THE PAIR OF MULTIVIBRATOR TRANSISTORS, THE VALUES OF SAID IMPEDANCE MEANS AND CAPACITORS BEING SUCH AS TO CAUSE SAID MULTIVIBRATOR TO OSCILLATE AT AN AUDIO FREQUENCY, MEANS CONNECTING THE ELECTRODE OF A FIRST ONE OF SAID MULTIVIBRATOR TRANSISTORS, ELECTRODE OF A FIRST ONE OF SAID MULTIVIBRATOR TRANSISTORS, AN AMPLIFIER TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELECTRODES, MEANS DIRECTLY ELECTRODE OF THE SECOND ONE OF ELECTRODE TO THE COLLECTOR ELECTRODE OF THE SECOND ONE OF SAID MULTIVIBRATOR TRANSISTORS, SAID COLLECTOR ELECTRODE OF THE SECOND MULTIVIBRATOR TRANSISTOR HAVING A FIRST POTENTIAL WHEN THE MULTIVIBRATOR IS NOT OSCILLATING OF A VALUE TO BIAS SAID LAST-NAMED BASE ELECTRODE FOR RENDERING SAID AMPLIFIER TRANSISTOR SUBSTANTIALY IN A CUTOFF CONDITION AND HAVING ALTERNATE FIRST AND SECOND VALUES OF POTENTIAL WHEN THE MULTIVIBRATOR IS OSCILLATING TO ALTERNATE THE BIAS OF SAID LAST-NAMED BASE ELECTRODE FOR ALTERNATELY RENDERING SAID AMPLIFIER TRANSISTOR IN A CURRENT-CONDUCTING SIGNAL-AMPLIFYING CONDITION, IMPEDANCE MEANS CONNECTED BETWEEN THE LAST-NAMED EMITTER ELECTRODE AND SAID SECOND TERMINAL, A LOUDSPEAKER CONNECTED BETWEEN THE LAST-NAMED COLLECTOR ELECTRODE AND SAID FIRST TERMINAL, AND MEANS FOR VARYING THE IMPEDANCE OF AT LEAST ONE OF SAID VARIABLE IMPEDANCE CIRCUITS THEREBY CAUSING SAID MULTIVIBRATOR TO OSCILLATE AND PRODUCE AN AUDIBLE SOUND AT SAID LOUDSPEAKER. 